1. Field of Invention
The instant invention generally relates to screw-type self-tapping fasteners. More particularly, the present invention relates to fasteners having multiple lead cutting threads that enhance the holding power of the fastener. While the present invention is directed generally to the field of masonry fasteners, it can be readily understood that application of the invention can be extended to other fasteners and other materials for use therewith.
2. State of the Art
Screw-type fasteners for fastening fixtures and various attachments for masonry and other materials are well known. Fasteners of this type generally include a helical cutting thread formed on the shank of the fastener, which acts to cut and tap the bank of a predrilled hole as the fastener is turned into the hole. The resistance of this fastener to axial pullout forces represents its holding power.
The term masonry is generic to all stone-like building materials, such as concrete and brick. When masonry is exceptionally hard, such as masonry whose aggregate is formed of granite, the torque required to turn the fastener into the predrilled hole is very high; so high, in fact, that the fastener may break.
To create a fastener capable of being screwed into exceptionally hard masonry, prior art fasteners have been provided with a helical thread having a V-shaped cross-sectional configuration in which the flanks of the threads intersect at an included angle of approximately 50 to 65 degrees. While this type of thread is capable of cutting into hard masonry, it is relatively fragile and may rupture.
Other prior art fasteners have a sharp-crested helical thread in which notches are formed in the crests of the thread to facilitate embedment of the crests in the bank of a predrilled hole. Aggregate particles cut from the bank of the masonry hole by the notches are collected in a reservoir in the space between successive convolutions of the thread. Since the particles are collected in this manner, they reduce torsional friction. Additionally, the retention of the particles in the reservoirs can enhance the pull out force of the fastener.
Yet another prior art self-tapping masonry fastener is provided with a helical cutting thread surrounding the shank of the fastener. The cutting thread is formed by a pair of parallel helical ridges with a depressed groove therebetween, which serves to collect substrate debris removed by the cutting action. Thus, even if particulate debris collected in the groove in the helical cutting thread were compacted, it would only serve to resist displacement of the helical thread with respect to the corresponding female thread cut into the bank of the hole. Nevertheless, this would not serve to significantly enhance the holding power of the fastener.
As evidenced by the above mentioned prior art fasteners, there is a recognized need for a more effective cutting edge, especially for self-tapping fasteners.
Accordingly, it is an object of the present invention to provide an effective cutting edge for fasteners.
Another object of the present invention is to provide self-tapping fasteners with a reinforced cutting edge.
It is a further object of the present invention to provide a cutting insert for fasteners.
It is yet a further object of the present invention to provide a combination fastener with cutting insert.
It is still another object of the present invention to provide a process of manufacture of a cutting insert for fasteners and/or a combination fastener with a cutting insert.
These and other objects of the present invention will be apparent in the following description.
The present invention provides a cutting insert for fasteners including a shape having an outline conforming to at least a portion of a contour of a cross-section of an end of a fastener. Additionally, the insert may have at least one thread protrusion for cutting a groove to thereby provide a track into which threads of the fastener would follow.
The present invention also provides a process of cutting insert for fasteners and/or a combination fastener with a cutting insert including steps of providing a flat sheet of a material from which the cutting insert is punched or stamped. Additional steps are included to provide a fastener with a slit at its tip. Yet another step includes stamping the material to provide the cutting insert shaped to fit into the slit at the tip of the fastener, and placing the cutting insert into the slit.
Additionally, the present invention provides a combination fastener and cutting insert, including a fastener having a slit at its end and a cutting insert having a shape with an outline conforming to at least a portion of a contour of a cross-section of the end of the fastener.